1. Field of the Invention
Embodiments disclosed herein relate generally to instrumentation of ram blowout preventers. More specifically, embodiments disclosed herein relate to the direct measurement of position, velocity, and rate of movement of the ram in a ram blowout preventer.
2. Background
Well control is an important aspect of oil and gas exploration. When drilling a well, for example, safety devices must be put in place to prevent injury to personnel and damage to equipment resulting from unexpected events associated with the drilling activities.
The process of drilling wells involves penetrating a variety of subsurface geologic structures, or “layers.” Occasionally, a wellbore will penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with the kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high pressure region to a low pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. Such “blowouts” may result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and substantially injure or result in the death of rig personnel.
Because of the risk of blowouts, devices known as blowout preventers are installed above the wellhead at the surface or on the sea floor in deep water drilling arrangements to effectively seal a wellbore until active measures can be taken to control the kick. Blowout preventers may be activated so that kicks are adequately controlled and “circulated out” of the system. There are several types of blowout preventers, the most common of which are ram blowout preventers and annular blowout preventers (including spherical blowout preventers).
Ram blowout preventers typically have a body and at least one pair of horizontally opposed bonnets. The bonnets are generally secured to the body about their circumference with, for example, bolts. Alternatively, bonnets may be secured to the body with a hinge and bolts so that the bonnet may be rotated to the side for maintenance access. Interior of each bonnet is a piston actuated ram. The rams may be either pipe rams (which, when activated, move to engage and surround drill pipe and well tools to seal the wellbore), shear rams (which, when activated, move to engage and physically shear any drill pipe or well tools in the wellbore), or blind rams (which, when activated, seal the bore like a gate valve). The rams are typically located opposite of each other and, whether pipe rams, shear rams, or blind rams, the rams typically seal against one another proximate a center of the wellbore in order to completely seal the wellbore.
The rams are generally constructed of steel and fitted with elastomeric components on the sealing surfaces. The ram blocks are available in a variety of configurations allowing them to seal a wellbore. Pipe rams typically have a circular cutout in the middle that corresponds to the diameter of the pipe in the hole to seal the well when the pipe is in the hole; however, these pipe rams effectively seal only a limited range of pipe diameters. Variable-bore rams are designed to seal a wider range of pipe diameters. The various ram blocks may also be changed within the blowout preventers, allowing well operators to optimize the blowout preventer configuration for the particular hole section or operation in progress. Examples of ram type blowout preventers are disclosed in U.S. Pat. Nos. 6,554,247, 6,244,560, 5,897,094, 5,655,745, and 4,647,002, each of which is incorporated herein by reference in their entireties.
Knowledge of the well conditions is extremely important to maintaining proper operation and anticipating future problems of the well. From these parameters, a well may be more effectively monitored so that safe conditions can be maintained. Furthermore, when an unsafe condition is detected, shut down of the well can be appropriately initiated, either manually or automatically. For example, pressure and temperature transducers blowout preventer cavities to may indicate or predict unsafe conditions. These and other signals may be presented as control signals on a control console employed by a well operator. The operator may, for example, affect the well conditions by regulating the rotating speed on the drill pipe, the downward pressure on the drill bit, and the circulation pumps for the drilling fluid. Furthermore, when closure of the BOP rams is desired, it is useful for the operator to have accurate knowledge of where each ram is positioned.
One device that has been employed in the past to develop a signal indicative of the relative position of component parts located in an enclosed housing (not necessarily in a blowout preventer housing) is a potentiometric transducer. Such a device employs one or more sensors that are subject to wear and inaccuracies in the presence of a harsh environment. Moreover, such sensors are subjected to being lifted from the surface of whatever is being tracked, which causes inaccuracies. Also, a loss of power often causes distorted readings because these devices operate incrementally, adding or subtracting values related to specific turns or segments of wire to a previous value. Moreover, devices such as these are notoriously poor high speed devices. Thus, potentiometric measurement would not be useful in accurately determining the position parameter of ram movement. Furthermore, potentiometric transducers are not suitable for use in high speed applications, which renders them of little to no use in ram monitoring applications.
In addition, incremental measuring devices that merely measure intermediate movement have the inherent shortcoming of having to be reset to a baseline in the event of a power failure as well as not providing the precision that is attendant to continuous measurement.
In order to improve the accuracy of measuring the location of the rams, magnetostrictive sensors have been used to monitor and/or control the position of the rams. As described in U.S. Pat. Nos. 5,320,325 and 5,407,172, which are hereby incorporated by reference, the piston driving arm of the ram is placed parallel to a stationary magnetizable waveguide tube. A magnet assembly surrounds the waveguide tube and is attached to a carrier arm that is attached to the tail of the piston.
In U.S. Pat. Nos. 7,023,199, 7,121,185, and 6,509,733, a magnetostrictive sensor is mounted in an internal opening of a sensor port. The sensor has a pressure pipe extending into the internal cavity of the cylinder body and telescopically received in a passage in the rod of a piston and rod assembly.
The positioning of the magnetostrictive sensors in each of the above described patents is less than optimal. For example, in U.S. Pat. No. 7,023,199, because the sensor extends into the cavity of the cylinder body, maintenance to be performed on the sensor unit necessarily requires that the ram not be in operation. The attachment of the sensor and magnets using a carrier arm in U.S. Pat. No. 5,320,325, although not invading the cavity of the cylinder body, may lead to inaccurate measurement of ram positions and may increase the expense of ram BOP fabrication.
Therefore, it is a feature of the present invention to provide an improved apparatus for precisely measuring the location or position of a ram or ram piston in a blowout preventer.
Accordingly, there exists a need for improved apparatus for precisely measuring the location or position of a ram or ram piston in a blowout preventer.